Conventionally, gas-insulated electric equipment such as a gas-insulated switchgear (GIS), a gas-insulated bus (GIB), and so on in which insulating gas is sealed are provided at an electric power system. In the gas-insulated electric equipment, a center conductor is stored in a grounded metal tank in which the insulating gas is sealed, and insulation between the metal tank and the center conductor is maintained.
However, in case of a gas-insulated electric equipment using SF6 gas as the insulating gas, liquefaction of the sealed SF6 gas occurs and internal sealed gas pressure is lowered under a low-temperature surrounding environment lower than −25° C., and therefore, a problem in which insulation performance deteriorates occurs. Accordingly, the gas-insulated electric equipment is placed indoor where it does not become low-temperature to avoid the liquefaction of the SF6 gas when the gas-insulated electric equipment is applied under the low-temperature surrounding environment.
However, the gas-insulated electric equipment is necessary to be connected at outdoor to secure an insulation distance in the atmosphere when the gas-insulated electric equipment is necessary to be connected in the atmosphere to be connected to an overhead power line and a voltage transformer circuit. In this case, a part of the gas-insulated electric equipment leading to an air connection part is placed under the low-temperature surrounding environment.
In general, the sealed insulating gas is not liquefied when the conductor stored in the metal tank of the gas-insulated electric equipment is conducted because it is heated by heat generation of the conductor. On the other hand, a gas pressure of the gas-insulated electric equipment is lowered to approximately an atmospheric pressure because the liquefaction of the SF6 gas sealed at a high-pressure exceeding the atmospheric pressure occurs in accordance with lowering of a surrounding temperature when it is not conducted. It is impossible to maintain the insulation ability for a high impulse voltage such as a thunderstorm when the pressure of the insulating gas is lowered to approximately the atmospheric pressure.
Accordingly, in order to prevent that the insulation performance deteriorates caused by the liquefaction of the insulating gas under the low-temperature surrounding environment, a measure such that the gas-insulated electric equipment is heated by an external electric heat source and so on is proposed.
However, it is necessary to be constantly conducted to heat and operational electric power is lost in the conventional method heating by the external electric power source. In addition, there is a possibility in which reliability of a whole of the equipment deteriorates because a problem in which the liquefaction of the insulating gas occurs cannot be solved at a trouble time of the external electric power source.